1. Field of the Invention
The present invention relates to a medical leads and particularly to medical leads having unitary construction.
2. Description of the Related Art
Implantable leads form an electrical connection between a pulse generator or other electronic device and a tissue or structure in the body. For example, leads transmit electric signals used to stimulate cardiac or nerve tissue in one direction and signals generated by sensors placed in proximity to particular organs or tissues in the opposite direction. Leads typically include one or more electrodes at the lead's distal end. The electrodes are designed to form an electrical connection with a tissue or organ. In addition, most leads also include a lead connector at the lead body's proximal end. Lead connectors are adapted to electrically and mechanically connect leads to the pulse generators or other electronic medical devices. A conductor connects the electrode to the lead connector. Commonly, the conductor takes the form of a single or multifilar wire coil. Although, there is an increasing interest in using stranded cables as conductors. Regardless of the conductor's form, an insulating material typically surrounds the conductors. Spinal chord stimulation leads are typically formed with individually insulated conductors surrounded by a separate lead body tube. Together, the conductor and the insulating material form the lead body. The lead body couples the lead connector at the proximal end with the electrode at the distal end.
Present lead designs frequently electrically connect a separate electrode assembly to the distal end of the lead. This results in an electrical connection and a seam between the electrode assembly and the lead body. Other current lead designs add ring electrodes over the lead body's distal end. To access the wound conductors within the lead body, the conductors are pulled from the lead body for welding to the edge of the ring electrode. The removal of the conductors from the lead body may result in a breach of the lead body's insulator that must later be sealed creating a seam. These seams and other junctions provide a potential point for failure and the potential for electrical leakage. Therefore, a need exists for a lead having a seam-less or unitary construction.
Similar to electrode assemblies, present lead designs frequently couple a separate connector assembly to the proximal end of the lead. Again, the produces a seam between the connector and the lead body. Other connector designs may add ring electrodes over the lead body's proximal end. To access the wound conductors within the lead body, the conductors are pulled from the lead body for welding to the edge of the ring electrode. The removal of the conductors from the lead body may result in a breach of the lead body's insulator that must later be sealed creating a seam. Again, These seams and other junctions provide a potential point for failure and the potential for electrical leakage. Therefore, a need exists for a lead having a unitary construction.
Further, manufacturing leads is costly. A significant portion of the cost is allocated to electrically connecting the conductors to the various electrodes, sensors and connectors used in the industry. Forming a secure electrical junction has proven difficult and time consuming. Laser welds are commonly used to connect the conductors to the electrodes. The conductors are typically helically wound into a coil for increased reliability and flexibility. Band electrodes are typically connected to conductors by welding in an operation separate from the application of the lead body tube. Once the band electrodes are connected to the conductors, an extruded tube is placed over the conductor coil and welded band electrodes are connected to the lead body tube by insert molding or RF welding. Band electrodes may also be connected to a conductor by etching away a region of insulator, applying a coating of electrically conductive adhesive, and then placing the band electrode around the conductor. This etching method is complex, not amenable to automation, and expensive. Therefore, a need exists for a method that reduces complexity and is easily automated to reduce production costs.
In another method of attachment, band electrodes are electrically connected to coiled conductors by placing a soft metal in a hole cut into an insulating sleeve. An electrode is placed over the metal and crimped or swaged to bring the electrode, soft metal and coiled conductors into electrical contact and to secure the electrode the lead body. The crimping or swaging method of connection results in electrical connections between the conductor and the band electrode that may fail. Further, swaging to electrically connect an electrode to a conductor is time consuming and difficult to implement with the modern reduced diameter leads. Hence, a need exists for an improved manufacturing technique to secure band electrodes to conductors that reduces the time, complexity and cost while increasing reliability.
In addition, current manufacturing techniques frequently require adding elements, such as collars, when connecting a band electrode to a coil. The added elements increase the lead's diameter near the weld. In application, a uniform diameter weld would result in a smaller lead. A smaller diameter lead is desired to allow placement in restricted spaces such as the epidural space or cardiac veins to reduce the effects of implanted lead on the patient. Further, a smaller lead allows for a smaller introducer that reduces the trauma associated with implantation and similarly a smaller removal sheath when explanting the lead. Hence, there exists a need to reduce the diameter of the welds used to secure electrodes to conductors in implantable medical leads.
The present invention meets the above-referenced needs and provides other advantages and improvements that will be evident to those skilled in the